Comparison of Pain Relief and Block Success of Great Occipital Nerve Block Using Different Approach Method at C2 Level

Great occipital nerve (GON) block is commonly applied for the pain management of occipital neuralgia, migraine, and cervicogenic headache. The GON orginates from the medial branch of the dorsal ramus of the C2 spinal nerve with variable contribution from the C3 dorsal ramus. After emerging from the suboccipital triangle, the nerve courses cephalad in an oblique trajectory between the semispinalis capitis (SC) and obliqus capitis inferior (OCI) muscles. This area was recognized as a potential location for GON injury. The nerve then passes through the trapezius muscle and courses medial to the occipital artery as it ascends to innervate the posterior scalp.

Many practitioners perform GON injections using a conventional approach, relying solely on superficial bone-based anatomic landmarks to infiltrate local anesthetic and corticosteroid around the nerve at the level of the superior nuchal line.

Some clinicians also use fluoroscopy to confirm the location of bony landmarks. The ambiguity of these injections poses a risk of anesthetizing adjacent structures or injecting into vessels, such as the occipital artery. Very limited research has been done to quantify the risk of these injections, but a complication rate of 5% to 10% has been reported, including headache, dizziness, blurred vision, and syncope.

Ultrasound guidance is increasingly used to mitigate these risks and improve the efficacy of GON injections. Multiple studies have demonstrated successful ultrasound-guided GON blockade at the superior nuchal line and improvement in pain scores compared with nonguided injections.

C2 level GON block using ultrasound targets interfascial plane between OCI and SC muscles. However, a pain physician who begins ultrasound guided injections migth feel very difficult targeting interfascial plane exactly.

Since GON orginiates from deep space of suboccipital triangle, it is expected that injection within OCI muscle might have similar effect with the effect of injection into interfascial plane.

We assume that if the local anesthetics is injected within OCI muscle, the effect of GON block will be generated by the diffusion of injected local anesthetics.